Changes of mutagenicity and antimutagenicity of the lactic fermented soymilk after exposure to acid, bile salt and heating

BACKGROUND: Fermented soymilk, prepared with co-culture of Streptococcus thermophilus and Bifidobacterium infantis, possessed enhanced antioxidant and antimutagenic activities. Considering the possible alternation in functional properties, the mutagenicity and antimutagenicity of the prepared fermented soymilk against 4-nitroquinoline-N-oxide (4-NQO) and 3,2'-dimethyl-4-aminobiphenyl (DMAB) as influenced by acid (pH 2.0), bile salt and heat treatments were investigated using the Ames test. RESULTS: Untreated- and treated-fermented soymilk showed no mutagenic activity. After exposure to a pH of 2.0 for 20 or 60 min, the antimutagenicity of the fermented soymilk on 4-NQO and DMAB decreased, while still possessing ca 25.9-33.9% and 61.8-67.9%, respectively, of its original activity. Exposure of fermented soymilk to 1% bile salt resulted in a 10.8% reduction, and no reduction of antimutagenicity, against 4-NQO and DMAB, respectively. Heating the fermented soymilk at 55 C or higher for 10min caused a significant reduction in antimutagenicity on DMAB, while the antimutagenicity against 4-NQO remained stable until the temperature was raised to 65 degrees C. CONCLUSION: The fermented soymilk still possessed antimutagenicity after exposure to all the treatments examined. This further demonstrates the potential utilization of fermented soymilk as an ingredient in the preparation of healthy foods. 2008 Society of Chemical Industry.